1. Field of the Invention
The present invention relates to a pulse width modulation (PWM), and more particularly, to a vehicle-use cooling fan driving apparatus provided with a trouble sensing function for sensing constraint or a short when a problem occurs in two motors having a large capacity difference between them and which are connected in parallel and driven in PWM method.
2. Description of the Related Art
A conventional vehicle-use cooling fan control device 1, as shown in FIG. 1, has one end portion thereof an engine control unit 50 and a battery B, and the other end portion thereof a radiator motor 10 and a condenser motor 11.
Control device 1 is made up of a microcomputer 2 for receiving a motor rotation signal from engine control unit 50 and converting the received signal to a pulse width modulated signal, a driver transistor 3 for receiving the pulse width modulated signal from microcomputer 2 and driving two motors 10 and 11, a resistance 4 connected to a source of driver transistor 3 and which senses a current, and a comparator 5 for comparing the current sensed by resistance 4 with a reference voltage.
In thus-structured vehicle-use cooling fan driving apparatus, engine control unit 50 senses temperature of water coolant, operating state of air conditioner, and speed of vehicle and transmits an appropriate rotation speed of the cooling fan to control device 1. Subsequently, microcomputer 2 of control device 1 senses the rotation speed, and applies a control signal obtained by pulse width modulating a specific frequency to a gate terminal of motor driver transistor 3.
Thus, a current is applied to a radiator motor 10 and a condenser motor 11 as driver transistor 3 is turned on/off, thereby rotating motors 10 and 11 at a specific rotation speed.
At this time, the amount of current applied is determined by a ratio (D) of pulse width to a pulse cycle, applied from microcomputer 2 to the gate terminal of driver transistor 3.
The current which passes from battery B to motors 10 and 11 flows to a source terminal via the drain terminal of driver transistor 3, and flows again to a ground terminal via resistor 4.
Here, comparator 5 compares the size of the voltage generated from current sensing resistance 4 with a reference voltage, and decreases pulse width applied to the gate terminal of driver transistor 3 by a specific ratio (xcex94 D) when the size of the voltage generated from current sensing resistance 4 exceeds the reference voltage. Comparator 5 controls pulse width by repeatedly performing the above-described operation, thus preventing a current exceeding a predetermined value from being applied to motors 10 and 11.
However, in such a conventional method, size of current sensing resistance 4 increases in proportion to the total size of the maximum allowable current of motors 10 and 11, thereby causing a significant constraint on the total size of control device 1. In addition, an error may be caused when the amount of current applied to the motor is measured, since resistance value varies depending on heat generation of resistance 4.
Further, if the control device is mounted onto an electronic substrate, it is required that a special lead endurable for a high temperature has to be employed instead of a common lead when soldering, thereby causing a cost increase and a complicated process.
In a common vehicle, a radiator motor and a condenser motor have difference in capacity thereof (the radiator motor has a capacity approximately two times larger than the condenser motor). At a specific frequency of noise generated from a motor operation when the same motors are used, the two motors may interfere with each other, thereby causing a noise from a resonance. To avoid this, the radiator motor for cooling the coolant water of engine is larger than the condenser motor for cooling the refrigerant of air conditioner.
Meanwhile, as shown in FIG. 2, in a conventional method, when a pulse applied to the gate terminal of driver transistor 3 is turned on, the current flowing at current sensing resistance 4 is compared with a reference value. If the current flowing at current sensing resistance 4 is larger than the reference value, pulse width is decreased so as to be applied to the gate terminal. If the motor rotation speed is lower than the maximum speed, a current at the state where either of two motors is constrained does not flow exceedingly the reference current and is not sensed. Thus, a current keeps flowing to the constrained motor, and the motor is over-heated, which may cause a fire.
When the cooling efficiency is higher as winter times, number of times of motor rotation may not reach the maximum number of rotation. At this time, a current keeps flowing to the constrained motor, which causes an overheating of the motor.
Referring to FIG. 3, reference current (IREF) is determined within a range larger than the sum of stationary current of radiator (IRN) and stationary current of condenser (ICN) and smaller than the sum of constraint current of condenser (ICL) and stationary current of radiator (IRN).
Such a conventional method has a problem in that the abnormal current may not be sensed when the speed of motor is lower than the maximum rotation speed.
Therefore, it is an object of the present invention to provide a vehicle-use cooling fan driving apparatus adapting a pulse width modulation method (PWM) in which two fan motors are driven in parallel and a trouble of motor is sensed so as to enhance a stability of vehicle.